This book covers the crucial yet often overlooked fermentation process that transforms coffee beans after harvest. During the washing and drying stages, raw coffee beans are exposed to their environment, allowing microorganisms to naturally settle and break down nutrients in the mucilage layer. This intentional microbial digestion is well-known among coffee growers but remains unfamiliar to many coffee consumers. Starting with an overview of the coffee processing chain, the book then explores the critical steps of fermentation. It reveals how secondary metabolites produced by microorganisms play a significant role in shaping coffee's unique flavors. Each chapter provides detailed insights into various metabolic pathways and the key groups of microorganisms involved, connecting fermentation to every stage of coffee processing. The authors’ combined expertise and shared enthusiasm for coffee are reflected throughout this manuscript, offering readers a unique blend of practical and scientific perspectives on coffee fermentation. By the end, readers will understand that coffee, much like sauerkraut, sourdough, and kimchi, is a fermented product. This fermentation process is essential in creating the rich, complex flavours that make our morning cup of coffee so delightful.